1. Field of the Invention
The present invention relates to a photo-sensitive and heat-sensitive recording material using a diazo compound and a coupler as color developing components, and more particularly, relates to a photo-sensitive and heat-sensitive recording material of a yellow to blue color developing type that is excellent in terms of virgin stock storability and manifests high concentration of color generation in heat recording. Further, the present invention relates to a photo-sensitive and heat-sensitive recording material having high photo-sensitivity with respect to light of relatively short wavelengths (350 nm to 390 nm) within an ultraviolet ray range.
2. Description of the Related Art
A diazo compound is a compound having extremely high chemical activity, and reacts with a so-called coupler comprising a phenol derivative or an active methylene group, to form an azo dye easily. A diazo compound also has photo-sensitivity, and is decomposed by irradiation to lose its activity.
Therefore, diazo compounds have been conventionally used as light recording materials as represented by diazo copy (see "Shashinkogaku no kiso--Higinen Shashin Hen (Fundamentals of Photographic Engineering--Non-Silver Salt Photography Section)", pp. 89 to 117, 182 to 201, edited by the Photographic Society of Japan, Corona Publishing Co., Ltd., 1982).
Further, recently, diazo compounds are also applied for recording materials requiring fixation of an image, thus utilizing its nature wherein it is decomposed and loses activity by an action of a light. As a typical example, there has been proposed a light fixation type heat-sensitive recording material wherein a diazo compound and a coupler are heated according to image signals to be reacted to form an image, and then the image is fixed by irradiation (Hirotsugu Sato et al., Bulletin of the Image Electronics Society, vol.11, No.4, (1982), pp. 290 to 296, and the like).
However, this recording material using a diazo compound as a color developing element has a defect wherein shelf life thereof as a recording material is short since the activity of the diazo compound is very high and the diazo compound is thermally decomposed gradually to lose its reactivity even in dark places.
There are various methods suggested as a means for improving instability of the diazo compounds, and as one of the most effective means, a method in which a diazo compound is enclosed in a microcapsule may be listed.
As described above, the diazo compound is insulated from materials promoting decomposition such as water, a base and the like by being enclosed in the microcapsule. Therefore, the decomposition thereof is remarkably suppressed and shelf life of a recording material using this increases greatly (Tomomasa Usami et al., Bulletin of the Electronic Photography Society, vol. 26, No. 2, (1987), pp. 115 to 125).
In a general method for enclosing a diazo compound in a microcapsule, the diazo compound is dissolved in a hydrophobic solvent (oil phase), the resultant solution is added to an aqueous solution (aqueous phase) into which a water-soluble polymer has been dissolved and is emulsified and dispersed by a homogenizer or the like, and at the same time, a monomer or prepolymer which will form a wall material of the microcapsule is added to the oil phase and/or the aqueous phase, to cause a polymerization reaction at an interface of the oil phase and the aqueous phase, or a polymer wall is formed by deposition of a polymer, thereby obtaining the microcapsule.
These methods are described in detail in, for example, Asashi Kondo, Microcapsule edited by Nikkan Kogyo Shinbun Publishing (published in 1970), Tamotsu Kondo et al., Microcapsule edited by Sankyo Shuppan (published in 1977), and the like.
As a material of the formed microcapsule wall, various materials such as crosslinked gelatin, alginate, celluloses, polyurea, polyurethane, melamine resin, nylon resin and the like can be used.
In a case of a microcapsule having a wall composed of a material with a glass transition temperature like a urea resin and urethane resin wherein the glass transition temperature is slightly higher than room temperature, this capsule is called a heat-responsive microcapsule and is useful for a heat-sensitive recording material since the capsule wall is impermeable with respect to materials at room temperature and is permeable with respect to materials at a temperature equivalent to or greater than the glass transition temperature thereof.
Namely, by producing the recording material comprising a substrate having applied thereto a photo-sensitive and heat-sensitive recording layer containing a coupler and a base and the heat-responsive microcapsule containing a diazo compound, the diazo compound can be kept in stable condition for a long period of time and a color developed image can be easily formed by heating, and further, an image can be fixed by irradiation.
As described above, stability of a diazo compound can be remarkably improved by enclosing the compound in a microcapsule.
However, even if the diazo compound is insulated from materials promoting decomposition such as water, a base or the like by being enclosed in a microcapsule, the diazo compound itself is unstable and is decomposed by the action of a light. Therefore, even if enclosure into a microcapsule is assumed, it is indispensable to stabilize the diazo compound itself.
Thus, the present inventors have conducted various investigations regarding a structure of a stable diazo compound. As a result, it has been found that a benzenediazonium salt having an alkoxy group or aryloxy group at an ortho position of a diazonio group is photosensitive with respect to a fixation light of a relatively short wavelength (350 nm to 390 nm) within the ultraviolet ray range and has improved heat stability in comparison with a benzenediazonium salt without an alkoxy group or aryloxy group at an ortho position of the diazonio group (Japanese Patent Application Laid-Open (JP-A) Nos. 64-80588, 4-59288, 4-197782).
However, even if these diazonium compounds are used, when they are used after being stored for a long period of time, base portions may sometimes become colored; therefore, further improvement has been desired for extending shelf life.
Accordingly, an object of the present invention is to provide a photo-sensitive and heat-sensitive recording material that has excellent virgin stock storability, provides a sufficiently high concentration of color generation in the resulting color developed image, and reveals high photo-sensitivity with respect to light of a relatively short wavelength (350 nm to 390 nm) within the ultraviolet ray range.